1. Field of the Invention
This invention relates to cylinder locks of the type having a shell surrounding a cylindrical key plug which is rotated by a key received in the plug to actuate the lock. More specifically, the invention relates to such locks in which the key operates two or more independent locking mechanisms before the key plug can be rotated.
2. Description of Related Art
Cylindrical locks have a cylindrical shell surrounding a cylindrical key plug with a longitudinal key slot or keyway formed therein adapted to receive a key of a particular configuration. The interface between the key plug and the shell forms a shear surface and the key plug is prevented from rotating by the locking mechanism which projects a series of locking elements across the shear surface, preventing it from rotating until the correct key is inserted.
In a conventional cylindrical lock, there is a single locking mechanism in which the locking elements are a series of spring driven segmented pins (referred to herein as the top pins) having upper and lower halves received in top pin bores which project across the shear surface.
Generally, the upper half of each top pin extends across the shear surface whenever the key is removed from the lock to prevent the key plug from rotating. Notches of varying depth along the top of the correct key lift the top pins to the desired height to align the joint between the upper and lower half of each top pin with the shear surface. The key plug can then be rotated with the lower half of each top pin rotating with the key plug and the upper half remaining stationary with the shell.
The depth of the notches along the top of the key define a key code for the lock, and only keys having that code, i.e., only keys having notches of the correct depth in the proper sequence will move the top pins to the correct predetermined position to allow the plug to rotate. The key slot is generally shaped with a series of longitudinal wards which match corresponding wards on the key.
Locks of this conventional type are widely used, but all have limitations in the number of available combinations of the locking codes, the resistance to picking, the resistance to forcible entry and the limited security afforded due to widely available key blanks and duplicating equipment for these conventional locks.
The present invention provides a significantly improved level of security by adding one or more additional locking mechanisms to the primary locking mechanism of the type described above. The secondary (or tertiary, etc.) locking mechanisms are operated by corresponding locking codes cut in the form of depressions of varying depth along the sides of the key. The additional locking codes are particularly advantageous in constructing a family of locks in which all members of each family have an identical secondary or tertiary locking code and vary only in the primary code corresponding to the notches in the key.
This allows the owner of a number of related locks, for example a hotel owner locking hotel rooms, or a marina owner locking storage areas, to be assigned a unique secondary locking code (or a secondary/tertiary locking code combination) for all of his keys. The unique secondary code is cut into key blanks with specialized equipment. The primary locking code may be cut into the blanks with conventional equipment.
The additional locking mechanisms also provide additional pick resistance through the use of side pins which engage the depressions forming the secondary locking code on the key and superior resistance to forced operation through the use of one or more locking bars actuated by the side pins.
Beyond the improvements in pick resistance, forcible operation resistance, and increased locking code combinations, it is an object of the invention to keep the additional locking mechanisms as small as possible so that additional space remains in the key plug for other locking mechanisms of the same or different designs.
It is yet another object of the present invention is to provide a design in which the additional locking codes may be quickly and easily changed in the field.
A further object of the present invention is to provide a lock design in which the additional locking codes may be changed using only the original lock components, without requiring any new pieces. A particular advantage of the present invention is that the code may not only be changed in the field, it may be changed several times without the need to remove or replace any of the pins used in the secondary locking mechanism, which is a common source of error when rekeying large numbers of locks.
An even greater advantage is that the secondary codes may all be changed very quickly to alter the secondary codes in a reliably predetermined manner so that the owner of multiple locks may be provided with a new unique secondary code for all his keys. The new keys must be encoded with the new secondary (or secondary/tertiary) code, but retain their original primary code. To prepare the new keys, it is simply necessary to copy the primary code of the original keys onto the new key blanks provided with the new secondary/tertiary code. This can be done with widely available conventional key cutting machines once the new blanks are provided.
Even more advantageously, the present design allows the secondary/tertiary codes to be changed so that the original keys may be used and the new secondary tertiary codes cut into the original keys by deepening certain of the depressions forming the additional codes.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.